Sebastian Kuzminsky wrote:
> I got it off the J6 tool holder, and the J6 taper on the tool holder has 
> ~0.001 inches of runout now (measured with a DTI on the taper, while 
> mounted in the spindle and turning slowly).  I don't know what the 
> runout was before the crash, and I don't know what's acceptable.  Does 
> this seem reasonable, or should I scrap the tool holder too and look for 
> another?  My spindle has a QC-30 taper, which is somewhat unusual - tool 
> holders like this can be hard to come by.
>
>   
Welcome to the world of machining!  (and, its downside.)

The problem is if there is .001" runout at the jacobs taper, then there 
will be several
times that at the jaws of a mounted drill chuck, and WAY more than that 
at the
tip of some drill bit.  What you have is not runout, but wobble, and it 
will just
get worse farther from the spindle.  If this was R-8, it wouldn't make 
sense to
even think about replacing the arbor, they are so cheap sellers often 
throw them in
almost for free with a good chuck.  So, you could consider trying to 
re-cut the
taper, ON the CNC machine.  Use the spindle as a lathe, put a lathe tool 
in the
vise and compute the right taper angle.  For .001" TIR, there is only a 
.0005"
eccentricity, so you won't have to take off much material at all.

To do it right, you could install a die grinder or other powered spindle 
in the
vise, but to get up to the shoulder you'd need the grinder spindle to be 
vertical,
and you mention limited Z travel (but maybe not limited Z clearance, so this
might work).

Jon

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